This proposal is a continuation of the work designed to study the effect of cast immobilization and exercise training on the cytoarchitecture, biochemistry, and physiologic characteristics of reinnervating rat muscle. The histochemistry, biochemistry, and electromyography of control and two exercise trained groups was completed to date. The evaluation of normal controls compared to reinnervating rat muscle at 1, 2, 3, 4, and 6 weeks after bilateral crushing of the sciatic nerve was determined. Slow muscles appeared to be reinnervated sooner than fast muscles, suggesting that the recovery from neuronal damage may be related to specific muscles, rather than solely a function of fiber type characteristics. It also appears that the decrease in the rate of synthesis of proteins and subsequent recovery of protein concentration and ultimately in muscle weight occurs prior to reinnervation. The sciatic nerve was crushed bilaterally in adult rats in order to determine the effect of exercise initiated at 2 and 3 weeks post-crush. Both groups were sacrificed at 6 weeks post-crush, and the data were analyzed and compared with controls from muscle weight histochemistry, proteins, and electromyography. It appeared that exercise, initiated 3 weeks post-crush, facilitated the synthesis of myofibrillar proteins. The activity induced during the reinnervation phase appears to stimulate the development of high frequency discharges. This work is relevant to health problems because it will assist in understanding the clinical response to exercise training programs, initiated at various times after the onset of nerve regeneration. The goal for 1976-77 will be to complete the evaluation in the physiological characteristics of control reinnervating rat muscle in terms of contraction properties and the determination of the number of motor units at various stages during reinnervation. We will also continue the evaluation of the morphologic, biochemical and physiologic characteristics of trained reinnervating rat muscle. BIBLIOGRAPHIC REFERENCES: Jaweed, M.M., Herbison, G.J., and Ditunno, J.F.: Denervation and Reinnervation of Fast and Slow Muscles: A Histochemical Study in Rats. J. Histochem Cytochem 23:808-827 (1975).